Recently, many research works have been done on the bio-ceramic materials based CaO-SiO2 system. But, unfortunately the
data presented in these works are not enough to complete understanding the relation between the formed phases and the final
properties of the produced materials. It is highly important to understand the microstructure-properties relationship for developing
new bioceramics. This work describes the effect of magnesia in the presence of zirconia on the bioactivity, microstructure and physicomechanical
properties of calcium silicate composition adjusted at calcia/silica ratio(C/S) of 0.5. A mixture from calcium carbonate
and silica was conducted at C/S of 0.5. 20 wt.% of magnesia and 5-25 wt.% of ZrO2 were added. Each mixture was mixed with ethanol
in a planetary ball mill, dried, formed and fired at a temperature of 1325±5°C. Phase composition, FE-SEM, and physico-mechanical
properties of the fired specimens were determined and explained. The in vitro bioactivities of these specimens were investigated by
analysis of their abilities to form apatite in the simulated body fluid (SBF) for a short time (7 days) using SEM-EDS. The findings
indicated that the surface of the specimens containing 5 and 15 wt.% ZrO2 were completely covered by single and multilayered
hydroxyapatite (HA) precipitate typical to “cauliflower” morphology, respectively. The surface of the specimen containing 25 wt.%
ZrO2 did not cover, but there are some scattered HA precipitate. The differences among the results were rationalized based on the
phase composition. Vickers hardness and fracture toughness of the specimens of highly promised bioactivity were 2.32–2.57 GPa
and 1.80–1.50 MPa. m1/2, respectively. The properties of these specimens are similar to the properties of human cortical bone.
Consequently, these composites might be used as bone implant materials.